As a vehicle display device, there is a so-called head-up display, which allows a user sitting in a driver seat to visually recognize a virtual image by projecting a display image on a translucent member such as a front windshield of a vehicle and using the light of a display image reflected by the front windshield. In such a vehicle display device, a virtual image is visually recognized by a user sitting in a driver seat so that a virtual image is formed on a vehicle traveling direction side (vehicle front side) with respect to a front windshield of a vehicle. A general configuration of such a vehicle display device includes, for example, an image display unit for displaying a display image, a projection unit constituted by an optical system, including a concave mirror for projecting a display image onto a front windshield of a vehicle.
A user sitting in a driver seat of a vehicle equipped with such a vehicle display device is able to visually recognize a virtual image, giving information, for example, on the presence of other vehicles, obstacles, etc. on a road in front of the vehicle in a state superimposed on a scenery seen through a front windshield. As a position at which the virtual image is visually recognized moves upward in a vertical direction of the front windshield, the virtual image is viewed superimposed on a scene of a far side of the scenery seen through the front windshield. On the other hand, as a position at which the virtual image is visually recognized moves downward in a vertical direction of the front windshield, the virtual image is viewed superimposed on a scene of a near side of the scenery seen through the front windshield.
Here, the viewpoint position of the user sitting in the driver seat is not constant depending on the sitting height and seated posture of the user, and the likes. For example, when the position at which the display image is projected is fixed, as the viewpoint position of the user sitting in the driver seat becomes higher, the virtual image is superimposed on the scene of the near side of the scenery seen through the front windshield. Thus, as the viewpoint position of the user sitting in the driver seat changes, an object in the scenery where the virtual image is superimposed deviates, causing a possibility of giving an uncomfortable feeling to the user.
Therefore, for example, Patent Literature 1 discloses a head-up display device (vehicle display device), which adjusts a projection direction of an optical system, including a concave mirror of a projection unit, in accordance with a position in a vertical direction of a viewpoint of a user sitting in a driver seat of a vehicle. The vehicle display device disclosed in Patent Literature 1 includes a concave mirror actuator that adjusts a projection angle of a concave mirror of a projection unit, and a viewpoint detection camera that acquires a position of a viewpoint of a user sitting in a driver seat of a vehicle.
In the vehicle display device disclosed in Patent Literature 1, the concave mirror actuator is controlled such that a display image is projected upward in a vertical direction of a front windshield when the viewpoint position of the user sitting in the driver seat of the vehicle acquired by the viewpoint detection camera is high. On the other hand, in the vehicle display device disclosed in Patent Literature 1, the concave mirror actuator is controlled such that a display image is projected downward in a vertical direction of a front windshield when the viewpoint position of the user sitting in the driver seat of the vehicle acquired by the viewpoint detection camera is low. Therefore, in the vehicle display device disclosed in Patent Literature 1, even when the viewpoint position of a user sitting in a driver seat of a vehicle changes, it is possible to prevent a great displacement of an object superimposed with a virtual image in the scenery seen through the front windshield.